- provide plenty of white space around the words to reduce the density of the text
- - leave the right side of emails ragged - do not justify the text
- "chunk" your material -- by that I mean use short paragraphs so that no more than two paras are on the screen at any time, about 100 words. (http://www.writergazette.com/articles/article62.shtml shows exactly how it should be done for an ezine and will also give you some tips about getting published).
- for online articles, use headings and sub-heads, bullets, etc.
- double space between paras and bulletted lists
- use a large enough font that contrasts with a light background (microscopic or difficult-to-read fancy fonts might just result in a deletion from a recipient who reads for a living)
- use only one font - preferably Arial or Times New Roman (Verdana is trendy at the moment but not recommended by the tech-gurus).
Remember too that readers over 45 years, and that's most readers, need reading glasses and some have other visual challenges.... So these screen writing rules make a lot of sense even for emails to Aunt Agatha.